In this EUREKA project (RFA-GM-10-009), we will accelerate the development of knowledge towards a clinical approach to thwart invasive oral pathogens associated with periodontitis and candidiasis. Oral keratinocytes appear to protect against and suppress invasive pathogens using two compartmentalized, intracellular antimicrobial effector systems: calprotectin in the cytosol and LL-37 in endosomes. By targeting these effectors, we plan to use two approaches to augment keratinocyte intracellular resistance to invasive pathogens. We hypothesize that intra-keratinocyte resistance against invasive microbial pathogens can be increased by transient delivery of specific antimicrobial effector mRNAs (e.g., S100A8 and S100A9) or specific agonists (e.g., vitamin D analogues to upregulate LL-37). Avoiding the use of transgenes, we will use the unusual approach of introducing calprotectin and/or LL-37 mRNAs into the keratinocyte. For comparison, in some experiments we will stimulate cells with vitamin D analogues to upregulate LL-37. We will learn whether endosomal and cytoplasmic resistance against invasive microbes can be selectively augmented. To learn whether the application of these specific mRNAs or vitamin A analogues to intact tissues will prove efficacious, and to consider cytotoxic, proinflammatory immune, and carcinogenic side effects, we will concurrently model this system in human tonsil explants ex vivo. Collectively, the experiments will characterize vitamin D analogues and transfer of antimicrobial effector mRNAs for the mechanism and effectiveness in augmenting intracellular innate resistance to invasive oral pathogens in oral keratinocytes. Our strategy may prove to be a valuable compliment to vaccines and antibiotics for most common oral infections, which are not life threatening and have relatively low morbidity. For these infections, vaccines have an unacceptable risk-benefit ratio. Antibiotics promote the risk of microbial resistance and host allergy. Our approach would circumvent these concerns.